1. Field of the Invention
The present invention relates generally to underwater pelletizing systems and, more particularly, to a gas injection nozzle for use with such systems.
2. Description of Related Art
Those skilled in the art have found it beneficial, and sometimes necessary, to produce pellets that crystallize, either partially or fully. To help achieve that crystallization, the assignee of the present invention has disclosed the use of a nozzle through which pressurized air or other gas can be injected into the pellet slurry to help decrease the retention time of the pellets in the transportation liquid between the upstream pelletization process and the downstream drying and subsequent processes in U.S. Pat. No. 7,157,032; U.S. Patent Application Publication Nos. 2005/0110182 and 2007/0132134; World Patent Application Publication Nos. WO 2005/051623, and WO 2006/127698, all of which are owned by the current assignee of the present invention and are incorporated herein by reference as if fully set forth in their entirety.
Similarly, WO 2007/027877 discloses the use of a nozzle through which pressurized air or other gas can be injected into the pellet slurry to facilitate aspiration of the liquid from the pellets in the pellet slurry. Moisture content of the pellets is lowered by reducing the retention time of the pellets in the transportation liquid between the upstream pelletization process and the downstream drying and subsequent processes. The reduced retention time also results in more of the internal heat of the pellets formed being retained, and thus reduces the moisture available for uptake by the pellets. This application, also owned by the current assignee of the present invention, is also incorporated by reference herein in its entirety.
Under certain conditions, pellets can clump or form agglomerates during the pelletizing process. The formation of pellet agglomerates can have many causes, of which sticky pellets is both common and frequent. When these agglomerates form they have the tendency to get caught in so-called “hang-up points”, a term used herein to describe locations throughout the process where pellets and/or agglomerates of pellets tend to get hung-up and remain, often forming an obstructive build-up. As an example, agglomerates of pellets can form when “drooling”, excessive flow of molten material through the die holes, occurs at the die plate, thus creating an undesirably large pellet. Large pellets are not the only problem. Pellets of desirable size can create a problem as well. Sticky pellets, or pellets that are still soft, that come into contact with the nozzle can be “smashed” and stick to the nozzle due to their stickiness and the velocities at which they are traveling. Eventually more and more pellets come into contact with those stuck on the nozzle and pellets begin to adhere to each other creating a mass of pellets, also referred to as an agglomerate. Eventually the mass of pellets can become large enough to disrupt the flow of transport liquid and pellets through the transport pipe. This disruption can force the pelletization process to be stopped.
One such hang-up point has been found to exist in pelletization lines utilizing the apparatus and process of inserting pressurized gas described in the afore-identified patents and applications, namely the point at which the gas insertion nozzle is located within the pellet transport pipe. According to these prior embodiments, the nozzle used to inject the air is as illustrated in FIG. 1 and generally designated by the reference numeral 200. The prior art fixed nozzle tube 210 is attached, preferably by welding, into elbow 202 at juncture 214. This fixed nozzle assembly 200 cannot be removed to facilitate start-up. It can further serve as a potential source for occlusion by pellet agglomeration as it cannot be maneuverably positioned to permit free flow of the pellet slurry about the periphery of the fixed nozzle pipe 210. Similarly, the fixed position limits the degree to which the air or other gas being injected can be controlled through valve regulation.
Therefore, a need exists for a positionable nozzle that can be adjusted to optimize the crystallization and/or drying of pellets produced by an underwater pelletizing system.